This invention relates to an electric fuel pump in which the fuel pump and the fuel filter disposed within a fuel tank of a vehicle or the like are arranged in an integral structure.
FIG. 14 is a side view showing partly in section a conventional electric fuel pump disclosed in U.S. Pat. No. 5,391,062. FIG. 15 is a sectional view taken along line XV--XV of FIG. 14. FIG. 16 is a sectional view taken along line XVI--XVI of FIG. 15. FIG. 17 is a plan view showing a pump cover to which no abutment relief portion is provided.
In the figures 1 is an impeller of a disc-shape having formed in its outer peripheral portion a plurality of vane groove portions 1a extending in radial direction, 2 is a pump cover having a sliding surface 2a opposing to one side surface 1b of the impeller 1 with a small gap therebetween and supporting the impeller 1, 3 is a pump base having a sliding surface 3a opposing to the other side surface 1c of the impeller 1 with a small gap therebetween and supporting the impeller 1. 4 is a pump chamber of an arcuate belt shape extending along the outer peripheral portion of the impeller 1 at the outer side of the sliding surface 2a of the pump cover 2 and the sliding surface 3a of the pump base 3, and 4a is an inner side wall of the inner and the outer sides of the pump chamber 4. 5 is a fuel suction port disposed to the side of the pump cover 2 and 6 is a pump chamber outlet disposed to the side of the pump base 3. It is to be noted that pump casing 7 is composed of the pump cover 2, the pump base 3, the pump chamber 4, the fuel suction port 5 and the pump chamber outlet 6.
Also, as shown in FIGS. 15 and 16, a gap larger than the small gap defined in connection with the impeller 1 is provided in the inner circumferential side of the pump chamber 4 in the vicinity of the side 6a opposite to the pump chamber outlet 6 of the sliding surface 2a of the pump cover 2 as an abutment relief portion 2b with respect to the impeller 1, the end portion of the abutment relief portion 2b has a tapered portion 2c of a very gentle slope. In one embodiment, the angle .theta. (shown in FIG. 16) of the tapered portion 2c is about 168.degree.. 8 shown in FIG. 14 is a motor shaft to which the impeller 1 is fitted, 9 is an armature and 10 is a magnet. 11 is a cylindrical housing or an outer sheath which mounts the magnet 10 and to which the pump casing 7 is fitted thereon. It is to be noted that a motor portion 12 is composed of the motor shaft 8, the armature 9, the magnet 10 and the housing 11. 13 is a motor chamber of the motor portion 12 and 14 is a fuel discharge port.
In the conventional electric fuel pump having the above-explained structure, when the motor portion 12 is operated, the impeller 1 rotates to suck the fuel (not shown) from the fuel suction port 5, the sucked fuel being pressure-increased in the pump chamber 4, introduced through the pump chamber outlet 6 into the motor chamber 13 and discharged to the outside through the fuel discharge port 14.
In the conventional electric fuel pump of the foregoing arrangement, a leakage loss generates within the gap defined between the side surfaces 1b, 1c of the impeller 1 and the sliding surfaces 2a, 3a of the pump cover 2 and the pump base 3 contacting to the side surfaces 1b, 1c and between the side 6a opposing to the pump chamber outlet 6 and the fuel suction port 5, i.e., the dam portion 2a -1. In order to prevent the decrease of the discharge efficiency of the pump due to this leakage loss, the gap in the thrust direction between the side surfaces 1b, 1c of the impeller 1 and the sliding surfaces 2a, 3a is made very small. Therefore, when the fuel pressure within the pump chamber 4 is increased due to the rotation of the vane grooves 1a toward the pump chamber outlet port 6 from the fuel suction port 5, the impeller 1 tends to be brought into contact with the position f the sliding surface 2a of the pump cover 2 in the vicinity of the side 6a opposing to the pump chamber outlet 6 in the pump casing 7 by the pressure unbalance between that about the pump chamber outlet 6 in the pump casing 7 and the fuel suction port 5 in the pump casing 7. When no abutment relief portion 2b is provided in the pump cover 2, as shown in FIG. 17, the sliding surface 2a of the pump cover 2 around the side 6a opposing to the pump chamber outlet 6 of the pump casing 7 is subjected to generation of sliding scares 15. In the conventional apparatus, the abutment relief portion 2b is provided at this region thereby to try to prevent the contact of the impeller 1.
However, as shown in FIG. 15, the dam portion 2a -1 is disposed only in the intermediate portion of the side 6a opposing to the pump chamber outlet 6 and the fuel suction port 5 in order to prevent decrease of the discharge efficiency of the pump due to the leakage loss generated between the side 6a opposing to the pump chamber outlet 6 and the fuel suction port 5. Therefore, at the position of the dam portion 2a -1 where no abutment relief portion 2b is provided, the impeller 1 is brought into contact with the pump casing 7. As a result, the rotation frictional resistance of the impeller 1 increases, the rotation of the motor 12 decreases and the electric current consumption increases, whereby the discharge efficiency of the electric fuel pump is disadvantageously decreases.